3D Imaging Through Hair-Thin Optical Fiber
Researchers have developed an endoscope that enables 3D imaging at near video rates through a single multimode fiber the diameter of a human hair. In the future, the technology can be used for everything from industrial inspection to environmental monitoring and has the potential to revolutionize medical imaging. The system was developed by an international team of researchers led by the University of Glasgow’s optics group. The holographic endoscope technology has been developed by Prof. Tomáš Čižmár for over a decade, and it is one of the most prominent activities of the Fiber Research and Technology department at the Leibniz Institute of Photonic Technology. The researchers published their findings in the renowned journal Science.
„Together with our research partners, we have succeeded in developing a very thin fiber endoscope with which we can record scenes standing up to several meters away,“ Tomáš Čižmár summarizes the results of the international research team. „We achieve this by combining our microendoscopes with the time-of-flight light method researched by our colleagues in Glasgow.“
„When light moves through an optical fiber, it doesn’t come out the other side in the same shape. Instead, it gets completely scrambled, therefore sending images through the fiber itself doesn’t work,“ Tomáš Čižmár explains. „We have explored a method to structure the laser light entering the fiber so that a single point of light appears at the end of the fiber. We use this to scan the scene to be recorded pixel by pixel, measuring the light intensity at each point. This information is then assembled on a computer to create a two-dimensional image.“
The Glasgow researchers complement microendoscopy with a time-of-flight technique to obtain depth information in addition to 2D reflectance images. Their technique determines depth by measuring the round-trip time of a laser pulse reflected from the scene. „By using a pulsed laser, the travel time of the light is measured, and thus it reveals the distance of each pixel in the image. The precise time-of-flight measurement technology enables the system to create complete 3D point clouds, similar to LiDAR,“ explains Dr. Sergey Turtaev, a scientist in the Holographic Endoscopy group at Leibniz IPHT.
The 3D images can be captured with millimeter-scale resolution and offer frame rates high enough to perceive motion in near video quality: The researchers image moving objects located several meters in front of the end of a fiber about 40 centimeters long with a core diameter of 50 micrometers, at frame rates of about 5 hertz.
Currently, the multimode fiber must remain in a fixed position after calibration. As a next step, the researchers will look at how to shorten the calibration time to allow the fiber endoscope to be moved, bent, and twisted. „With our publication in the journal Science, we have reached an important milestone. We are now researching how to maintain and use the flexibility of the fiber. Once the technology is developed far enough, it can be used in a variety of practical applications, such as autonomous driving, safety applications and ultimately in medicine,“ Tomáš Čižmár gives an outlook.
The project is a collaboration between physicists at the University of Glasgow, University of Exeter, Fraunhofer Centre for Applied Photonics Glasgow, Leibniz Institute of Photonic Technology, Germany, and the Institute of Scientific Instruments of the Czech Academy of Sciences.
The paper, titled ‚Time-of-flight 3D imaging through multimode optical fibres‘, is published in Science.
The research was supported by funding from Engineering and Physical Sciences Research Council (EPSRC), UK National Quantum Technology Programme (UKNQTP), European Research Council (ERC), Royal Academy of Engineering and the Royal Society.
Daan Stellinga, David B. Phillips, Simon Peter Mekhail, Adam Selyem, Sergey Turtaev, Tomáš Čižmár, Miles J. PadgettTime-of-flight 3D imaging through multimode optical fibers, Science, 9 Dec 2021, Vol 374, Issue 6573, pp. 1395-1399 https://doi.org/10.1126/science.abl3771
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